EMG and nerve conduction study: what to expect

If a doctor has suggested an EMG for your foot or leg, it is normal to feel a little nervous. Most people’s main questions are the same: what exactly happens, how much will it hurt, and what can the results tell us? Here is a plain-language walk-through.

What the tests measure

Nerve conduction studies and EMG record electrical activity, and together they can help show whether a nerve is affected, where the trouble is, and how severe it is.^[5] They are especially helpful for telling a pinched nerve in the foot from a nerve-root problem in the lower back, and for identifying a body-wide neuropathy.^[6,5]

• Nerve conduction study (NCS). Small stickers (electrodes) are placed on the skin over a nerve and the muscle it supplies. A small, brief electrical pulse is given, and the test records how fast and how strongly the signal travels.
• Electromyography (EMG). A very thin needle is placed into a muscle to record its electrical activity at rest and as you gently tighten it.

Both are done in an outpatient setting and are performed by another specialist, often a neurologist or a physiatrist (a rehabilitation physician). At the Lower Extremity Nerve Institute we don’t perform them ourselves. We coordinate the testing when it is needed and review the results with you.

What it feels like

The electrical pulses of the nerve conduction study feel like brief tingles or taps. The needle part can be uncomfortable for a moment.

Two research findings are reassuring:

• In a randomized trial of the pain of needle EMG, the way the needle was handled mattered. With small needle movements of about a millimeter or less, the pain from a standard concentric needle was significantly lower. The study also found that pain was not predicted by the examiner’s experience, the person’s gender, whether they had had an EMG before, or how much pain they said they could tolerate.^[1]
• In another randomized trial, people who were given written information beforehand reported less anxiety during nerve conduction studies. Women who received the information also reported less pain from both the nerve conduction study and the EMG.^[2]

In other words, being told clearly what will happen can make a real difference. It is fine to ask the technician to explain each step, tell you when the needle is going in, and pause if you need to.

How to get ready

• Follow the instructions from the testing office. Ask if there is anything to do or avoid beforehand.
• Tell them about the medicines you take, especially blood thinners, and about any implanted devices such as a pacemaker.
• Bring a list of your symptoms, and any previous test results or reports. They can save you a repeat test.
• Let the person testing you know where your symptoms are so they can focus on the right nerves and muscles.

What the results can and can’t tell you

The results can help locate a problem and show how severe it is. They can also suggest how likely the nerve is to recover.^[5,7]

What they cannot do is prove that a nerve is fine. In an evidence-based review of tarsal tunnel syndrome, nerve conduction studies were abnormal in some, but not all, people with the condition, and the actual sensitivity and specificity could not be determined.^[3] Another study noted that the sensitivity of electrodiagnostic testing for tarsal tunnel syndrome is just over 50%. In that series, people with normal and abnormal tests improved by similar amounts after surgery on the nerve.^[4] Guidelines for testing nerves in the foot are also limited.^[8]

This is why results are never read on their own. They are combined with your history and a physical examination. For many foot nerve problems, the examination is the most useful step. See nerve testing for foot pain for the full picture, including imaging and blood tests.

When testing is most useful

Testing is most helpful when it can change the diagnosis or the plan. For example:

• when it isn’t clear whether the problem is in the back, the leg or the foot (see sciatica or a foot nerve problem?)
• when a body-wide neuropathy is suspected
• when there is weakness, such as foot drop, and we need to know how much nerve damage is present
• when symptoms have continued after treatment and the source is still unclear

When to see a specialist

Consider an evaluation if burning, tingling or numbness in your foot lasts more than a few weeks, or if you have had tests that were normal but your symptoms haven’t gone away.